A trunked communication system, such as a Land Mobile Radio (LMR) system, is one in which mobile or portable user terminals, such as mobile telephones, portable radios or radios on vehicles (herein collectively referred to as “mobile stations”) can communicate via a network infrastructure. The network infrastructure generally includes fixed installations, for example, one or more fixed base stations and/or various sub-systems that manage and control the system. The mobile stations operating in trunked communication systems share radio frequency (RF) communication channels (also referred to as traffic channels) and are configured to send and receive calls on shared traffic channels. A site controller, for example a base station, manages transmissions sent from mobile stations on free traffic channels whose availability is determined by the site controller. The site controller assigns one or more channels as the “control channel”, wherein on the control channel, the site controller transmits, to the mobile stations, system information and other data associated with the shared traffic channels. The mobile stations continuously monitor the control channel so that each mobile station knows when to transmit call information on a free traffic channel.
During an emergency, the site controller may become unavailable. For example, during a natural disaster such as an earth quake or fire emergency, the base station serving as the site controller may be damaged. When the base station is unavailable, there is no way to manage the system traffic and ensure that each mobile station knows when to transmit or receive call information on a free traffic channel. During this time, although the mobile stations may also be configured to reach each other in talk around mode, in the talk around mode a mobile station can only communicate directly with another mobile station operating on the same RF channel. By using only one channel for communications in talk around mode, the mobile stations cannot share traffic channels and otherwise engage in trunking operations.
The mobile stations may further be configured to form an ad-hoc network. An “ad-hoc network” refers to a self-configuring network of geographically-distributed mobile stations connected by wireless links (e.g., radio frequency communication channels). The ad-hoc networks could be built based on a wide band protocol, such as Wi-Fi, Bluetooth, or Zigbee. The mobile stations can communicate with each other over a wireless media without the support of an infrastructure-based or wired network. Links or connections between these mobile stations can change dynamically in an arbitrary manner as existing mobile stations move within the ad-hoc network, as new mobile stations join the ad-hoc network, or as existing mobile stations exit the ad hoc network. One characteristic of the mobile stations is that each mobile station can directly communicate over a short range with mobile stations which are a single “hop” away. Mobile stations in direct communication are sometimes referred to as “neighbor mobile stations.”
Although the mobile stations may be configured to form an ad-hoc network when the base station is unavailable, even if the mobile stations have access to the shared traffic channels, it is difficult to select one or more mobile stations to act as the site controller because of the dynamic nature of ad-hoc networks. Furthermore, because mobile stations in the ad-hoc network, can directly communicate over a short range, there is a need to repeat information when a sending mobile station is more than a hop away from a receiving mobile station.
Accordingly, there is a need for an improved method and apparatus for determining a suitable group of mobile stations in an ad-hoc network to manage trunking operations in the ad-hoc network when the site controller is unavailable.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.